Magnetic piston mercury switch



March 7, 1967 I H. HURVITZ 3,308,405

MAGNETIC PISTON MERCURY SWITCH Filed Aug. 50; 1965 INV EN TOR HYMAN HURVITZ 2! b v Q ATTORNEYS United States Patent 3,308,405 MAGNETIC PIST N MERCURY SWITCH Hyman Hurvitz, Washington, D.C., assignor to Fifth Dimension Inc., Princeton, N.J., a corporation of New Jersey Filed Aug. 30, 1965, Ser. No. 483,707

' 5 Claims. (Cl. 335-52) The present invention relates generally to mercury switches and, more particularly, to mercury switches employing one or more capillary columns of mercury in a mercury wettable capillary tube, the mercury being activated by a mass of magnetic powder operating as a piston.

It is an object of the invention to provide a simple, easily fabricated. mercury switch capable of rapid action, which is of small dimensions and which is position insensitive and shock and vibration insensitive.

Briefly describing the invention in a preferred form, it includes two mercury wettable capillary tubes joined by a ring of mercury unwettable material. Within the ring is a mass of fine magnetic powder (iron) in granular form. The iron is not mercury wettable. The tubes contain mercury and are terminated by insulators containing electrodes located adjacent the ends of the mercury columns formed by the tubes. The magnetic powder is moved magnetically as a piston to move the mercury columns and thus open and close circuits to the electrodes. The electrodes are mercury wettable, so that adhesion of mercury to the tubes and to the electrodes renders the switch insensitive to shock, vibration and position.

It is an object of the invention to provide a miniature mercury switch including a mass ofiron granules emploved as a piston.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 of the drawings is a view in section taken through a switch arranged according to the invention; and

FIGURES 2-5 are views in section representing variants of the system of FIGURE 1.

It is known to design capillary mercury switches in which a slug moves within a mercury column and acts as an electrode. The slug is elongated and extends almost, but not quite, between two stationary electrodes. Therefore, the slug has considerable mass. Moreover, the slug is rather complex in structure, i.e. mercury wettable only at its ends and capable of transferring mercury along its length. Therefore, it is costly and a source of possible failure.

In accordance with the present invention, no slug is employed in a miniature mercury switch, but rather a mass of magnetic particles of micron size, all independent of each other, and mercury unwettable. This mass can be very light, i.e. of capillary diameter, but of about a diameter length axially of the switch. Use of iron powder simplifies switch construction, and renders feasible a smaller switch and thus a faster switch.

Instead of moving an electrode, as in the prior art, the iron powder is used to distort or move a column of mercury sufiiciently to make and break contact between the mercury and a stationary electrode.

Another feature of the invention is that a deficiency of mercury can be employed, so that the ends of the mercury columns are concave when the switch is open and are rendered convex or fiat at the electrode end to close the switch contacts.

The magnetic powder may be excessively fine and since it is not wettable provides a piston which is substantially Patented Mar. 7, 1967 mercury impervious but capable of moving mercury. The cohesion of the latter maintains the integrity of the column with respect to the piston, the spaces between particles being insufiicient to permit passage of the iron particles through the free mercury surface which is presented to the piston.

The problem of moving mercury toward an electrode is solved by the powdered iron piston, but the question remainswhat force will withdraw the mercury against the adhesion of the electrode to open the switch. This force is, in part, supplied by the adhesion of the tubes enclosing the mercury, and the insufficiency of mercury to fill the tubes, the available mercury wets the wettable surface but leaves a concave volume (meniscus) at each end of the tube. This occurs because, for mercury, adhesive forces are greater than cohesive forces, for suitable wettable metals, as platinum. If the deficiency is considerable, i.e. if the meniscus is very deep, the mercury column will reform when the piston releases. But, if the deficiency is very slight, there may be insufiicient adhesive force in the tubes to reform the column against the adhesive forces of the electrode. At the same time, the size of the electrode is important. A small electrode provides little adhesion and a large electrode provides large adhesion. As the piston withdraws the mercury tends to follow, since the alternative is to generate a low pressure area at the junction of piston and mercury. If follows that several forces contribute to opening of the switch. But it also follows that the forces can be so proportioned that the switch will be self-latching, despite Withdrawal of magnetizing force at the piston, or so that the switch is open, unless held closed.

In the drawings, 10 is a first capillary tube made of platinum. 11 is another such tube. Tubes 10 and 11 are joined by an insulating ring 12, preferably of glass. Within ring 12 is a mass 13 of powdered iron, individual particles being of micron size. This mass 13 provides a magnetically actuable piston which is deformable. The tubes 10 and 11 are each almost filled with mercury columns 15, 16, the mercury columns res-ting against piston 13 at their interior ends and forming menisci 17, 18- at their free ends. The menisci would naturally form at both ends of each tube, but sufficient iron is supplied to fill the interior menisci. The open ends of tubes 10 and 11 are closed off with glass insulators 19, 20, through which extended mercury wettable electrodes 21, 22 to positions almost in contact with the menisci or slightly interiorly of the cavities these form. Two energizing coils 23 and 24 surround ring 12.

In FIGURE 1, both electrodes 21 and 22 are normally in open circuits, by providing a considerable deficiency of mercury and therefore deep menisci 17, 18. The coils 23, 24 are positioned to move piston 13 in opposite senses, and thereby to move the mercury columns 15, 16 in opposite deviations. When the movement is to the left column 15 contacts electrode 21. When the coils are both de-energized, the columns return to normal position because forces of cohesion at the tubes 10, 11 exceed those at the electrodes. Energization of both coils 23, 24 does not move piston 13.

In FIGURE 2, the mercury columns are denoted by reference numerals 15a, 16a. Electrode 21a is longer than 22, and sufliciently long to maintain a circuit at electrodes 21a, with coils 23, 24 de-energized. Coil 24, when energized, moves piston 13 to the right, to provide a circuit for electrode 22 and to open the circuit of electrode 21.

If enough mercury is supplied, or if the electrodes are long enough, FIGURE 3, to render both electrodes 21, 22 in contact with mercury normally, the switches can be operated to open a contact when the appropriate one of coils 23, 24 is energized. The switch can then be '3 bistable, but can be closed at both ends by energizing both of coils 23, 24.

It will be noted that the piston 13 provides no bias. It tends to remain where it is positioned. It can be moved by the coils or by the mercury, or both, and remains Where the balance of forces moves it. Since ring 13 is not wettable, there is no tendency for the mercury columns to transfer. The shape of the piston 13 can conform to the forces applied to it. Therefore, the mercury columns will assume a position for which the opposing adhesive and cohesive forces generated by the mercury columns and the wettable tubes balance. But a wide variety of operating characteristics can be achieved by selecting quantities of mercury and lengths of electrodes.

The mercury columns can further be biased in either sense by a permanent magnet associated with coils 23, 24 and appropriately positioned. In the system of FIG- URE 4, electrode 22 is in contact with mercury when coils 23, 24 are de-energized, since permanent magnet 25 is offset to the right of powdered iron mass 13. Coil 24a is symmetrically located and hence centralizes the mass and opens both electrodes. Coil 23a pulls the mass to the left and closes electrode 21.

In FIGURE 5, the wet areas of each of electrodes 21b and 22b is so great that enough adhesive force is developed at the electrodes to latch the switch when operated in either sense.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. A mercury switch comprising a first capillary mercury wettable tube, a second mercury wettable capillary tube, a mercury unwettable ring joining said tubes end to end, a mass of mercury unwettable iron powder located within and filling said ring, said tubes having free ends, insulating closures secured to said ends, electrodes extending through said closures, magnetic coils for moving said mass of iron powder, and a column of mercury in each of said tubes extending into proximity to said electrodes,

said column of mercury extending into operative relation with said mass of iron powder.

2. The combination according to claim 1 wherein the quantity of mercury is selected to leave menisci at the free remote ends of said columns of mercury, the adjacent ends of said columns of mercury being in contact with said mass of iron powder.

3. A mercury switch comprising a mercury wettable capillary tube, a capillary column of mercury substantially filling said tube, a contact located adjacent one end of said column of mercury and opposed to said column of mercury, a magnetic piston located wholly at the other end of said column of mercury, and means for moving said magnetic piston to distort said column of mercury sufficiently to make and break electrical contact between said column of mercury and said contact.

4. A mercury switch comprising a mercury wettable capillary enclosure, a column of mercury within said enclosure, said column of mercury being arranged to enable formation of a meniscus at one of the ends of said column of mercury, an electrode located adjacent said meniscus but spaced from said one of the ends, and means for stressing said column of mercury sufficiently to deform said one of the ends selectively into and out of contact with said electrode by deforming said meniscus, said means for stressing including a magnetic piston located in operative relation to exert force with respect to the other of said ends of said column of mercury. S. The combination according to claim 4 wh'ereinsaid means for stressing is a deformable piston.

References Cited by the Examiner UNITED STATES PATENTS 3,144,533 8/1964 Donath 200-112 BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, Assistant Examiner. 

3. A MERCURY SWITCH COMPRISING A MERCURY WETTABLE CAPILLARY TUBE, A CAPILLARY COLUMN OF MERCURY SUBSTANTIALLY FILLING SAID TUBE, A CONTACT LOCATED ADJACENT ONE END OF SAID COLUMN OF MERCURY AND OPPOSED TO SAID COLUMN OF MERCURY, A MAGNETIC PISTON LOCATED WHOLLY AT THE OTHER END OF SAID COLUMN OF MERCURY, AND MEANS FOR MOVING SAID MAGNETIC PISTON TO DISTORT SAID COLUMN OF MERCURY SUFFICIENTLY TO MAKE AND BREAK ELECTRICAL CONTACT BETWEEN SAID COLUMN OF MERCURY AND SAID CONTACT. 